As for a connection structure between a flat electric cable and terminal fittings that is used when the flat electric cable is mounted in a connector housing, for example, the structure described in Patent Document 1 has conventionally been known. Patent Document 1 discloses a flat harness that includes a connector housing in which a plurality of terminal accommodation rooms accommodating terminal fittings are aligned in a width direction of a circuit structure (a flat electric cable) and provided in a plurality of levels. Since such a connector housing is provided, the flat harness is reduced in size.